Recovery of metals



United States Patent 0 RECOVERY OF METALS Albert L. Jafie, Philadelphia,Ya.

No Drawing. Application January 2, 1957 Serial No. 632,000

11 Claims. (c1. 134-2 This application is a continuation-in-part of myapplication No. 618,192 for Separation of Metals, filed October 25,1956.

This invention relates to the recovery of scrap metals. Moreparticularly, it relates to the recovery of copper based articles, suchas radiators and wires, which are presented for recovery coated orotherwise in contact with relatively low melting point metals, such assolder, tin, Babbitt metal, zinc, antimony and their alloys and similarlow melting point metals and alloys. Articles of manufacture which areto be subjected to this recovery process may also be presented forrecovery associated with other materials, e.g., tinned or untinned wirewhich is presented coated with insulation. This insulation is usuallypolyethylene, polyvinyl chloride (PVC), or rubber which may or may notbe combined with fabric. This invention further relates to the recoveryof aluminum, particularly aluminum wire, which is presented for recoveryassociated with the low melting point metal or alloy or insulatingmaterials as described above.

' When copper or aluminum objects, such as those described above, arepresented for recovery, the object is to remove the associated foreignmetals, alloys and other materials in as rapid, inexpensive and thorougha method as possible whereby copper or aluminum will be made availablein the purest form possible.

The principal present method for removing solder (a tin-lead alloy) fromcopper or copper-alloy bases such as, for example, automobile radiators,has been sweating the radiator in ovens and vibrating to remove thesolder. Such a method is disclosed in U.S. Patent 1,826,755. From a viewpoint of reclaiming the copper, the sweating process has disadvantages.It is difiicult to thoroughly remove all the solder material. If thetemperature is high enough to remedy this, the danger of alloying thetin component with the copper is encountered. This makes the copperbrittle and also decreases its scrap value. Furthermore, oxides of boththe copper base and the low melting point metals are produced resultingin a lower grade copper scrap.

Where, throughout this specification and claims, the word copper orcopper-based is used, it is meant to include all copper base alloys suchas brass (85% copper, 15% zinc) or bronze (copper and tin) where a majorportion of the alloy is copper.

It is an object of this invention to provide a method for theinexpensive removal of foreign, relatively low melting point metals andalloys and insulating materials from copper, copper based and aluminumarticles of manufacture whereby a suitable scrap copper, copper al-103;, or aluminum metal may be obtained.

It is an object of this invention to remove tin, lead, solder andBabbitt metal from copper and brass articles.

It is another object of this invention to remove insulating materialsand relatively low melting point metals from copper, copper alloy andaluminum bases by a method comprising immersion in a bath of fusedsodium hydroxide producing a high-grade scrap.

EROS

u W m 2,891,881

Patented June 23, 1959 It is yet another object of this invention toremove insulating materials and relatively low melting point metals byimmersion in a bath of fused sodium hydroxide and alkali metal hydridesand alkali metal chlorates, nitrates, chromates, manganates,permanganates, peroxides and dichromates.

These and other objects will be made clear in the following detaileddescription.

Some of the copper and copper alloy articles from which the low meltingmetals may be removed are tinplated copper wire, light copper spouting(light gauge roofing materials), sheet copper, painted and plated yellowbrass stock, nickel-plated brass, plated or soldered copper tubing,electrotype shells, honeycomb radiators, nickel-plated red brassspigots, valves and pipes, and babbitted bearings. These articles arenot to be construed as exhaustive of this inventions uses but are merelyillustrative of some of the many common commercial uses.

Copper wire plated with tin may be stri ed of its tin bympro'cess'accordifig to this invention. Ilie copper wire, without anyprior heating or other treatment is immersed in a bath of sodium hydrideand sodium hydroxide. The proportion of sodium hydride in the bathshould be at least 1.0% and preferably at least 1.6%-2.0%. Theproportion of NaH may be as high as 20.0%, but about 2.0% is workableand commercially feasible. A NaH concentration of only 0.5% has beenfound unsatisfactory. The temperature of the bath should be betweenabout 675 and 775 F. preferably in the range of 700 to 750 F. Thetemperature and concentration conditions of the bath are the same as inthe prior art disclosures for pickling or de-scaling ferrous materials.The tin-plated copper wire is immersed in the bath for a period ofapproximately 10 to 15 minutes. This time may vary depending on theconditions, such as the thickness of the plate. When withdrawn andwashed or rinsed with hot water to remove the sodium hydroxide coatingor phlegm, the copper was found to be clean and to be of 99.98% purity.

It has been known to use sodium hydride in a fused bath of sodiumhydroxide to remove oxide scale from steel, iron, and steel alloys suchas stainless steel. Such a process is disclosed for example, in U.S.Patent No. 2,377,876. The materials producing the sodiumhydroxide-sodium hydride bath are marketed by several companies. Forexample, the El. du Pont de Nemours and Co., Inc. supplies theappropriate chemicals and information as to the requisite apparatus. Thedu Pont process is described as being applicable to the removal of scalefrom many metals and alloys such as nickel, Monel, Stellite, titanium,and cobalt bearing alloys. Other producers of hydride de-scalingmaterials are Metal Hydrides, Inc., Beverly, Mass, and U.S. IndustrialChemicals Co., New York, N.Y.

The sodium hydride-sodium hydroxide bath is generally prepared asfollows: A container of sodium hydroxide, equipped with heatingelements, is heated to a temperature at which the sodium hydroxidefuses. Associated with the container is a generator box, into whichmetallic sodium is charged and into which hydrogen is bubbled. Sodiumhydride is produced and mixes into the sodium hydroxide bath. Theconcept of the production of this hydride bath is not deemed part of thepresent invention and the use of other existing methods and apparatusfor NaH production is contemplated. The apparatus and method for hydridebath production is well known in the art and it is not deemed necessaryto describe this method and apparatus in detail in this disclosure.Methods and apparatus for the provision of sodium hydride baths aredisclosed, for example, in U.S.

3 Patent No. 2,353,026, the booklet entitled Du Pont Sodium HydrideDe-scaling Process, published by Du Pont Company or a Technical Bulletin507C published by Metal Hydrides, Inc., Beverly, Mass. The bath shouldbe substantially anhydrous.

Example Copper wire coated with tin was placed, Without prior treatment,into a fused bath of 1.8% NaH in NaOH. The bath was maintained at atemperature of 750 F. After minutes in the bath, the wire was withdrawnand found to be completely clean of tin. The treated copper was 99.98%pure.

Example 2 200 pounds of tin coated copper wire without prior treatmentwas immersed in a fused bath of 1.6% NaOH at 720 F. After 10 minutes thewire was withdrawn, flushed or rinsed with hot water to remove thecoating or phlegm of NaOH. The purity of this copper wire was found tobe 99.9%. This process was then repeated in the same fused bath and wasfound to be again successful.

It was feared in Examples 1 and 2 that the tin would go into solution inthe NaOH and therefore recoat subsequently treated samples but thisrecoating was found not to occur. It is not completely understood whythis process should remove the tin plate so efiiciently. Merely exposingtin-plated copper wire to indirect heat of temperature equal to that ofExamples 1 and 2 does not produce completely de-tinned copper wire.

Where copper or brass articles totally or partially coated with solderare to be de-soldered it has been found .that a preliminary step to theNaH bath is desirable. The article should first be subjected to indirectheat of approximately 900. By indirect heat is meant heat sup pliedelectrically or in any other manner wherein the work is not contacted bydirect flame. The work is preheated at this temperature for a period oftime which will vary depending on the character of the article to betreated (such as the thickness of solder), but it has been found thatfor an article such as a copper honeycomb radiator, one hour pre-heatingis satisfactory.

After the pre-heating stage the work piece is transferred immediately toa bath of fused NaOH and NaH. The temperature and NaH concentration ofthe bath is the same as described above in connection with detinningcopper wire.

The period of immersion in the fused bath may vary depending on theconditions (as the amount of material to be removed, the temperature ofthe bath, and the concentration of the bath). It has been found that forpieces such as soldered radiators a period of 10 to 20 minutes issatisfactory.

Example 3 A copper radiator, having soldered connections, was preheatedin indirect, electric oven heat at 900 F. for one hour. The radiator wasthen immersed in a fused bath of NaOH with a 2.0% NaH at a temperatureof 750 F. It was maintained in this bath for 20 minutes. The piece wasthen withdrawn, shaken, water quenched and hot water rinsed. The piecewas then pickled for 10 minutes in 10% NHO at room temperature, rinsed,and air dried.

Example 4 A copper radiator having soldered connections was preheated inindirect, electric oven heat at 900 F. for one hour. The radiator wasthen immediately immersed in a fused bath of NaOH with 1.8% NaH at atemperature of 750 F. It was maintained in this bath for 20 minutes. Thepiece was withdrawn, shaken, water quenched, and hot water rinsed. Thepiece was then pickled for 10 minutes in 10% Nl-IO at room temperature,rinsed, and air dried.

The copper reclaimed by means of Examples 3 and 4 tested to a purity of99.90%. Substantially the same treatment as described in Examples 3 and4 was performed on a work piece made of brass (approximately copper, 15%zinc). After treatment, the brass piece also showed as complete freedomfrom lead and tin as did the copper work piece. The steps of quenching,rinsing, and acid pickling are not alleged to be novel per se. Suchsteps have often been performed in connection with sodium hydridedescaling and in de-scaling in general. The acid treatment stepbrightens the reclaimed copper or copper alloy material, but is not anessential step to the inventive process herein desclosed.

In addition to soldered metal coatings, Babbitt metal (alloys ofantimony, lead and tin) coatings may be successfully treated with thisprocess. This class of alloys is used, for example, in bushings,bearings, and electrotype shells. It has been found that pre-heatingelectrotype shells with indirect heat at temperatures from 700 to 900 P.will result in the sweating of much of the white metal alloy from thecopper shell, leaving a substantial remainder. Immediate immersion ofthe shell into a fused NaOH-NAH bath of the same range of temperature,strength and times as in the preceding examples, results in the completeremoval of the white metals from the copper piece.

Attempts to completely remove lead, tin, antimony and various alloysfrom copper or copper alloy bases by heatings alone are not completelysatisfactory. If the heating is of high enough temperature and of longenough duration to effectively remove all the low melting metal,undesirable results may occur. The low melting metals may form a surfacealloy with the copper thus greatly reducing the commercial valuethereof. Another possibility is the production of oxides of copper onthe sur-- face, which also greatly down grades the commercial value,resulting in burnt copper.

If the heating conditions are moderated to avoid these problems, the lowmelting metals are not completely removed from the base. They often meltout into a thin adherent film on the base metal. In the aspects of thepresent invention wherein a pre-heating step is used, the material neednot be heated to the point of danger of alloying or burning. Pre-heatingto a point at which some coating still remains on the base and thenrelying on the hydride bath to remove the remainder of the coatingproduces a clean copper. As indicated above, for example, a temperatureof about 900 F. is satisfactory for soldered copper articles. The exactpre-heat temperature is not highly critical, but the temperature rangeis important. A pre-heat temperature of 600 F. was found whollyunsatisfactory; a temperature of 900 F. was completely satisfactory inthe case of solder. For Babbitt metal, a range of about 700 F. to 900'F. is satisfactory.

A reason that indirect heating is preferred for the preheating step isthat direct heat may produce hot spots which tend to oxidize or alloywith the base material.

It is not completely understood why the present preheating and hydridebath process is so successful. It has been suggested that in thepre-heating step, some low melting material is simply melted away, andthat thereafter a film or other formation of the coating metal remainsadherent to the copper or copper alloy base, and is retained or dammedby a crust of low melting alloy oxide which prevents flow of the innerfilm. It is thought that upon immersion in the hydride bath, the oxidecrust may be reduced, and since high temperature is present in the bath,the remaining film is free to flush away.

It is understood, of course, that this is merely a hypothesis. In thecase of immersion of tin-coated articles without pre-heating, anotherexplanation must be found. It may be that the hydride bath is effectivewhen the coating is thin, either initially as in the case of tinnedwire, or because of the pre-heating (sweating) step.

The term coating is understood to mean complete or partial covering ofthe copper or copper alloy base metal by a relatively low melting-pointmetal or alloy.

While sodium hydride is commercially feasible, other metal hydrides, aslithium hydride and potassium hydride may also act under conditions oftemperature and concentration suitable to their known chemicalproperties.

It has been found that although the use of sodium hydroxide incombination with sodium hydride or other alkali metal hydrides is aneiiicient scrap recovery process, caustic alkali, such as sodiumhydroxide, alone will also perform the desired function. The plain,fused, substantially anhydrous caustic bath may be used in the samemanner as that illustrated in Examples 1-4 except that the time oftreatment is substantially lengthened.

The term low melting-point metals is understood to mean the metals andtheir alloys.

The scope of this invention is to be determined by the appended claimsand not by the specific examples and illustrations set forth in thedescription.

Example 5 Copper wire coated with tin was placed without prior treatmentinto a fused bath of substantially anhydrous fused NaOH. The bath wasmaintained at a temperature of 750 F. After 30 minutes, the wire waswithdrawn and found to be completely free of tin. The treated coppertested to 99.98% purity.

The same temperature and other conditions as described above inconnection with a sodium hydroxidesodium hydride bath are applicable tothe plain sodium hydroxide bath with the proviso that a substantiallylonger period of immersion is required to obtain equal results;furthermore, the operating temperature of the bath is not limited by thepresence of sodium hydride. It is necessary when using sodium hydride,to maintain the bath temperature no higher than those described above inorder to avoid loss of the hydride from the solution. When using causticalkali alone, the upper temperature limit is limited only by thephysical properties of the caustic alkali and may therefore besubstantially higher. It has been found that a practicable minimumtemperature is 750 F. While sodium hydroxide is commercially feasible,other alkali metal hydroxides, such as potassium hydroxide, may be used.

In addition to using a caustic alkali alone or a mixture of a causticalkali and an alkali hydride, this invention contemplates the use of acaustic alkali bath with any one of many substantially anhydrousoxidizing agents. Sodium hydroxide with an oxidizing agent is availablefrom the Hooker Electrochemical Company, Niagara Falls, N.Y., and isknown under the trade name of Virgo Descaling Salt.

A copper or aluminum article associated with a relatively lowmelting-point metal or alloy, such as tin, solder or Babbitt metal, isimmersed in a fused substantially anhydrous bath comprising a causticalkali (preferably sodium hydroxide) and an oxidizing agent. Suitableoxidizing agents are alkali metal and alkaline earthchlorates...nitrates, manganates, permanganates, chromates, drchro- Representativeof these agents are mates and eroxides. sodium nitrate, sodium chlorateand potassium chlorate. The proportion of oxidizing agent may be from120% and preferably 5-10%. The temperature may vary within wide limits,preferably from about 600 F.-l000 F. and preferably should be about 900F. The chemical compositions and their operating temperatures per se arenot alleged to be new. They are known in the art and are disclosed inconnection with a difierent process in US. Patent Re. 22,887.

The article to be recovered is immersed in the bath for a periodsuflicient to completely remove the foreign metal or alloy. The time ofimmersion has been found to be about 5-15 minutes, depending on thearticle. The article may be water washed and dipped in dilutednon-oxidizing acid, such as hydrochloric acid, to complete the removalof any undesirable material, including caustic alkali phlegm.

Example 6 A length of tinned copper wire was immersed for 5 minutes in afused bath of 10% sodium nitrate in NaOH at a temperature of about 1000F. After 5 minutes in the bath, the wire was withdrawn and found to becompletely free of tin.

Example 7 A length of tinned copper wire was immersed in a fused bath of10% sodium nitrate at a temperature of about 900 F. After about 10minutes, the wire was withdrawn from the bath and was found to becompletely free of tin.

It was heretofore believed that such baths could not be used to removelow melting metals and metal alloys. It was believed that the tin wouldgo into some form of solution in the bath and rapidly render itineffective. It has been found that, in fact, the solution retains itseffectiveness for repeated dippings. The use of a sodiumhydroxide-sodium nitrate bath to recover scrap is somewhat lessexpensive and less hazardous than a sodium hydroxide-sodium hydride bathand more efiicient and faster than a plain sodium hydroxide bath.

Much wire scrap is presented for recovery with insulation on it. Suchinsulation is usually polyethylene, polyvinyl chloride or combinationsof these two in discrete layers of rubber. It has been found that suchinsulated wire may be immersed in any of the baths disclosed herein,whether or not it also has a coating of tin or other low melting metaland is removed as clean, high purity copper or aluminum wire as the casemay be.

On immersion in the bath, the insulation is rapidly destroyed. Thenature of this destruction depends on the material comprising theinsulation, being either a burning or melting process. The desiredresult, removal of the insulation from the metal to be recovered, isaccomplished regardless of the type of insulation. The follow ingexamples are representative of application of the present process to theremoval of insulation. Similar results are obtained with all of thebaths described herein.

Example 8 A length of copper wire, covered only with insulationconsisting of a layer of polyethylene and a layer of polyvinyl chloride,was immersed in a bath of fused, substantially anhydrous sodiumhydroxide and 10% sodium nitrate at a temperature of 950 F. The wire wasstripped clean in 1 minute, 40 seconds.

Example 9 A length of copper wire, tinned and insulated with a layer ofpolyethylene and a layer of polyvinyl chloride, was immersed in a bathof fused, substantially anhydrous 90% sodium hydroxide and 10% sodiumnitrate at a temperature of 950 F. The wire was stripped clean of bothinsulation and tin in 5 minutes.

The increased time in Example 9 was required to remove the tin. Ofcourse, in this process, the insulation is lost and cannot be recovered.This it not too serious a drawback, since the scrap price of the metalis far higher than the scrap value of the plastic or other insulationand the rapidity and ease of the process justifies the loss of theinsulation.

The problem of removing insulating coatings from wire has been a seriousone in the scrap recovery industry and the provision of the presentmethod by which insulating coatings and foreign low melting metals andalloys are simultaneously removed from copper, copper alloys andaluminum based metals is a significant economic improvement in the artof scrap recovery. It is understood that the essence of this inventionis the use of the described baths for the purpose of removing metals andinsulation from scrap. The baths themselves are admittedly known in theart, but have always heretofore been used solely for the removal ofscales and oxides from metals, never for the removal of metal itself.

The merit of this disclosure lies in the provision of a novel new usefor the known baths; the removal of metal from a base of dissimilarmetal and the removal of organic substances from a base of metal for thepurpose of facilitating the recovery of scrap metal.

I claim:

1. The method of removing a coating comprising both a relatively lowmelting-point metal and or insulation from articles made of material ofthe group consisting of copper and aluminum and mixtures thereofcomprising immersing said articles in a bath comprising fusedsubstantially anhydrous caustic alkali until said relatively lowmelting-point"nietals'afid organic insulation are removed, and thenremoving said articles from the bath, whereby a high grade scrap isobtained.

2. The method of removing a coating comprising both a relatively lowmelting-point metal and organic insulation from articles made ofmaterial of the group consisting of copper and aluminum and mixturesthereof comprising immersing said articles in a bath comprising fusedsubstantially anhydrous caustic alkali containing a substantial butminor proportion of an oxidizing agent stable therewith, at atemperature of 600 F.l000 F. until said relatively low melting-pointmetals and organic insulation are removed, and then removing saidarticles from the bath, whereby a high grade scrap is obtained.

3. The method as defined in claim 1 wherein the bath :Eisists solely offused substantially anhydrous caustic ali.

4. The method as defined in claim 2 wherein the proportion of saidoxidizing agent is from 1% to 20%.

5. The method as defined in claim 2 wherein the proportion of saidoxidizing agent is from 5% to 10%.

6. The method as defined in claim 2 wherein said oxidizing agent issodium nitrate.

7. The method of removing a coating of relatively low melting pointmetals from articles of the group consisting of copper and aluminumcomprising immersing said articles in a bath comprising fusedsubstantially anhydrous caustic alkali containing a substantial butminor proportion of an oxidizing agent stable therewith, at atemperature of 600 F. to 1000 F. until said relatively low melting pointmetals are removed, and then removing said articles from the bath,whereby a high grade scrape is obtained.

8. The method as defined in claim 7 wherein the proportion of saidoxidizing agent is from 1% to 20%.

9. The method as defined in claim 7 wherein the proportion of saidoxidizing agent is from 5% to 10%.

10. The method as defined in claim 7 wherein the oxidizing agent issodium nitrate.

11. The method of removing a coating of organic insulation from articlesof the group consisting of copper and aluminum comprising immersing saidarticles in a bath comprising fused substantially anhydrous causticalkali containing a substantial but minor proportion of anoxidizingagent stabile therewith, at a temperature 600 F. to 1000 F.until said organic insulation is removed, and then removing saidarticles from the bath, whereby a high grade scrap is obtained.

No references cited.

1. THE METHOD OF REMOVING A COATING COMPRISING BOTH A RELATIVELY LOWMELTING-POINT METAL AND ORGANIC INSULATION FROM ARTICLES MADE OFMATERIAL OF LOW GROUP CONSISTING OF COPPER AND ALUMINUM AND MIXTURESTHEREOF COMPRISING IMMERSING SAID ARTICLES IN A BATH COMPRISING FUSEDSUBSTANTIALLY ANHYDROUS CAUSTIC ALKALI UNTIL SAID RELATIVELY LOWMELTING-POINT METALS AND ORGANIC INSULATION ARE REMOVED, AND THENREMOVING SAID ARTICLES FROM THE BATH, WHEREBY A HIGH GRADE SCRAP ISOBTAINED.